Radiation sensor, method of forming the sensor and device including the sensor

ABSTRACT

A semiconductor device includes a semiconductor structure formed on a substrate, a gate dielectric formed on a first side of the semiconductor structure, and a dielectric layer formed on a second side of the semiconductor structure.

This Application is a Continuation Application of U.S. patentapplication Ser. No. 15/610,335, filed on May 31, 2017, which is aContinuation Application of U.S. patent application Ser. No. 15/198,426,filed on Jun. 30, 2016, now U.S. Pat. No. 9,722,125 B1.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a radiation sensor, and moreparticularly, to a radiation sensor which includes a fin structure and acharge collector dielectric layer formed on an outer side of the finstructure.

Description of the Related Art

Radiation sensors are conventionally used to sense the presence ofelectromagnetic radiation, such as gamma rays, X-rays and the higherenergy range of ultraviolet light. They may measure radiation in termsof accumulated dose (e.g., rad) or in terms of dose rate (e.g., rads perunit time). They have many applications, including in medical and spacetechnologies.

A metal oxide semiconductor field effect transistor (MOSFET) dosimeteris an example of a conventional radiation sensor. When a MOSFETdosimeter is irradiated, electron-hole pairs are generated within thegate oxide of the MOSFET by the incident radiation. Electrons quicklymove out of the gate electrode of the MOSFET while holes move towardsthe silicon/gate oxide interface where they become trapped in long termsites, causing a negative threshold voltage shift which can persist foryears. The difference in voltage shift before and after exposure can bemeasured, and is proportional to dose.

SUMMARY

In view of the foregoing and other problems, disadvantages, anddrawbacks of the aforementioned conventional devices and methods, anexemplary aspect of the present invention is directed to a radiationsensor that may be formed by modifying a vertical field effecttransistor (VFET).

An exemplary aspect of the present invention is directed to a radiationsensor includes a fin structure including semiconductor material formedon a substrate, a gate formed on an inner side of the fin structure, anda charge collector dielectric layer formed on an outer side of the finstructure.

Another exemplary aspect of the present invention is directed to amethod of forming a radiation sensor. The method includes forming aplurality of vertical field effect transistors (VFETs) on a logic regionand sensor region of a substrate, forming a mask on the logic region, soas to expose the sensor region, removing a gate from an outer side of apair of fin structures of a VFET in the sensor region, and forming acharge collector dielectric layer on the outer side of the pair of finstructures.

Another exemplary aspect of the present invention is directed to aradiation sensor. The radiation sensor includes a first source/drainregion formed on a substrate, a pair of fin structures includingsemiconductor material formed on the first source/drain region, a high-kdielectric layer formed on an inner side of the pair of fin structures,a metal gate formed on the high-k dielectric layer between the pair offin structures, a charge collector dielectric layer formed on an outerside of the pair of fin structures, and a second source/drain regionformed on an upper surface of the pair of fin structures.

With its unique and novel features, the present invention provides aradiation sensor that may be formed by modifying a vertical field effecttransistor (VFET).

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will be betterunderstood from the following detailed description of the embodiments ofthe invention with reference to the drawings, in which:

FIG. 1 illustrates a conventional vertical field effect transistor(VFET) 1;

FIG. 2A illustrates a radiation sensor 200, according to an exemplaryaspect of the present invention.

FIG. 2B illustrates a method 201 of forming a radiation sensor (e.g.,radiation sensor 200), according to an exemplary aspect of the presentinvention;

FIG. 3 illustrates a radiation sensor 300 according to an exemplaryaspect of the present invention;

FIG. 4 provides a graph 400 illustrating a property (e.g.,characteristic) of the radiation sensors 200, 300, according to anexemplary aspect of the present invention;

FIG. 5 illustrates a semiconductor device 501, according to an exemplaryaspect of the present invention;

FIG. 6 illustrates a method 600 of forming a radiation sensor accordingto an exemplary aspect of the present invention;

FIG. 7A illustrates a forming of a plurality of VFETs 700, 1700,according to an exemplary aspect of the present invention;

FIG. 7B illustrates an etching of the VFET 700, according to anexemplary aspect of the present invention;

FIG. 7C illustrates another etching of the VFET 700, according to anexemplary aspect of the present invention; and

FIG. 7D illustrates the forming of a charge collector dielectric layer790 (e.g., oxide layer) formed on the outer side 710 b of the pair offin structures 710 in the VFET 700, according to an exemplary aspect ofthe present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS OF THE INVENTION

Vertical transistors are being explored as a device option for furtherscaling of complementary metal oxide semiconductor (CMOS). However,conventional vertical transistors are not sensitive to radiation due tosuperior channel control by metal gates at both sides of fins.

FIG. 1 illustrates a conventional vertical field effect transistor(VFET) 1.

As illustrated in FIG. 1, the conventional VFET 1 has a fin structure 10(e.g., fin channel) formed on a substrate 5, and metal gates 20 a, 20 bformed on both sides of the fin structure 10 through the gate dielectric15 a, 15 b.

The conventional VFET 1 also includes a source region 30 formed on thesubstrate 5, the fin structure 10 being formed on the source region 30,and a drain region 40 which is formed on the fin structure 10. A bottomspacer 50 is formed between the metal gates 20 a, 20 b and the sourceregion 30, and a top spacer 60 is formed between the drain region 40 andmetal gates 20 a, 20 b. An interlayer dielectric 90 is formed on themetal gates 20 a, 20 b and the source region 30.

In the conventional VFET 1, the fin structure 10 is well-controlled byboth metal gates 20 a, 20 b. As a result, the conventional VFET 1 is notsensitive to radiation which is a very desirable quality for a VFETbeing used in microprocessors, but it precludes the VFET from being usedin radiation sensors.

Referring now to the drawings, FIGS. 2A-7D illustrate the exemplaryaspects of the present invention.

In particular, FIG. 2A illustrates a radiation sensor 200, according toan exemplary aspect of the present invention.

As illustrated in FIG. 2A, the radiation sensor 200 includes a finstructure 210 including semiconductor material formed on a substrate205, a gate 220 formed on an inner side 210 a of the fin structure 210,and a charge collector dielectric layer 290 formed on an outer side 210b of the fin structure 210. It should be noted that the dielectricmaterial which forms the charge collector dielectric layer 290 may alsobe formed on other parts of the radiation sensor 200 (e.g., on substrate205), and not just on the outer side 210 b of the fin structure 210.Thus, for example, the charge collector dielectric layer 290 may alsofunction as an interlayer dielectric. The fin structure 210, sometimesreferred to as fin channel, may include any suitable semiconductormaterial, including but not limited to, silicon, germanium, silicongermanium, silicon carbide, and those consisting essentially of compoundsemiconductors having a composition defined by the formulaAl_(X1)Ga_(X2)In_(X3)As_(Y1)P_(Y2)N_(Y3)Sb_(Y4), where X1, X2, X3, Y1,Y2, Y3, and Y4 represent relative proportions, each greater than orequal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 being the total relativemole quantity). Other suitable substrates include compoundsemiconductors having a composition Zn_(A1)Cd_(A2)Se_(S1)Te_(S2), whereA1, A2, B1, and B2 are relative proportions each greater than or equalto zero and A1+A2+B1+B2=1 (1 being a total mole quantity). The radiationsensor 200 may also include a gate dielectric 215 formed between thegate 220 and the inner side 210 a of the fin structure 210. The gate 220may include a conductive material such as a metal (e.g., tungsten,titanium, tantalum, ruthenium, zirconium, cobalt, copper, aluminum,lead, platinum, tin, silver, gold), a conducting metallic compoundmaterial (e.g., tantalum nitride, titanium nitride, tantalum carbide,titanium carbide, titanium aluminum carbide, tungsten silicide, tungstennitride, ruthenium oxide, cobalt silicide, nickel silicide), carbonnanotube, conductive carbon, graphene, or doped polycrystalline oramorphous silicon, germanium, silicon germanium, or any suitablecombination of these materials. The gate dielectric 215 may include anoxide such as silicon oxide, or a high-k dielectric material, or anycombination of these materials. Examples of high-k materials include butare not limited to metal oxides such as hafnium oxide, hafnium siliconoxide, hafnium silicon oxynitride, lanthanum oxide, lanthanum aluminumoxide, zirconium oxide, zirconium silicon oxide, zirconium siliconoxynitride, tantalum oxide, titanium oxide, barium strontium titaniumoxide, barium titanium oxide, strontium titanium oxide, yttrium oxide,aluminum oxide, lead scandium tantalum oxide, and lead zinc niobate. Thehigh-k may further include dopants such as lanthanum, aluminum. Thecharge collector dielectric layer 290 may include a dielectric such assilicon oxide, silicon oxynitride, silicon nitride, SiCO, SiOCN, SiCOH,SiBCN, or any suitable combination of those materials.

The radiation sensor 200 may also include a first source/drain region230 formed on the substrate 205, the fin structure 210 being formed onthe first source/drain region 230. The radiation sensor 200 may alsoinclude a second source/drain region 240 formed on an upper surface ofthe fin structure 210. The source/drain region regions 230 and 240 canbe doped with dopants such boron, gallium, indium, phosphorus, arsenic,antimony. The dopants can be incorporated in source/drain regions by anysuitable doping technique, including but not limited to, ionimplantation, gas phase doping, plasma doping, plasma immersion ionimplantation, cluster doping, infusion doping, liquid phase doping,solid phase doping, in-situ doped epitaxy, or any suitable combinationof those techniques.

The radiation sensor 200 may also include a bottom spacer 250 formed onthe first source/drain region 230, the gate 220 being formed on thebottom spacer 250, and a top spacer 260 formed on the gate 220, thesecond source/drain region 240 being formed on the top spacer 260. Thetop and bottom spacers may a dielectric such as silicon oxide, siliconoxynitride, silicon nitride, SiCO, SiOCN, SiCOH, SiBCN, or any suitablecombination of those materials.

As illustrated in FIG. 2A, the radiation sensor 200 may have a structuresimilar to the structure of a vertical field effect transistor (VFET)such as the conventional VFET 100 in FIG. 1. In an exemplary aspect ofthe present invention, the radiation sensor 200 may be formed by formingthe VFET 100 and then modifying the VFET 100 to replace the gate 20 b onone side of the fin structure 10 with the charge collector dielectriclayer 290.

Thus, the radiation sensor 200 may be referred to as a VFET radiationsensor (e.g., a VFET with a one-sided gate), where a gate dielectric(e.g., high-k dielectric layer) and gate (e.g., metal gate) is formedonly on one side of the fin structure. The other side of the finstructure is abutting the charge collector dielectric layer (e.g.,oxide) which server as the collector of radiation charges.

As illustrated in FIG. 2A, when radiation (e.g., electromagneticradiation, such as gamma rays, X-rays and the higher energy range ofultraviolet light) is incident on the charge collector dielectric layer290, radiation charges RC (e.g., radiation particles) may become trappedin a portion of the charge collector dielectric layer 290 adjacent tothe fin structure 210.

The portion of the charge collector dielectric layer 290 containing theradiation charges RC may thus serve as a back gate, modulating thetransistor characteristics (e.g., the threshold voltage (Vt)) ofradiation sensor 200. That is, for example, a threshold voltage Vt ofthe radiation sensor 200 may shift as a function of radiation dose(e.g., the amount of radiation to which the radiation sensor 200 isexposed, or the amount of radiation incident on the charge collectordielectric layer 290), and the gate 220 may be operable to sense theshifting of the threshold voltage (Vt) of the radiation sensor 200.

FIG. 2B illustrates a method 201 of forming a radiation sensor (e.g.,radiation sensor 200), according to an exemplary aspect of the presentinvention.

As illustrated in FIG. 2B, the method 201 includes forming (202) a finstructure including semiconductor material on a substrate, forming (203)a gate on an inner side of the fin structure, and forming (204) a chargecollector dielectric layer on an outer side of the fin structure. Inparticular, the forming of the gate may include forming the gate on boththe inner and outer sides of the fin structure, in which case, theforming of the charge collector dielectric layer may include removingthe gate from the outer side of the fin structure, and then forming thecharge collector dielectric layer.

FIG. 3 illustrates a radiation sensor 300 according to an exemplaryaspect of the present invention.

As illustrated in FIG. 3, the radiation sensor 300 is similar instructure to the radiation sensor 200, but includes a pair of finstructures 310 including semiconductor material formed on a substrate305. The radiation sensor 300 also includes a gate 320 formed on aninner side 310 a of the pair of fin structures 310, and a chargecollector dielectric layer 390 formed on an outer side 310 b of the pairof fin structures 310.

The radiation sensor 300 may also include a gate dielectric 315 formedbetween the gate 320 and the inner side 310 a of the pair of finstructures 310. The gate 320 may include a conductive material such as ametal (e.g., tungsten, titanium, tantalum, ruthenium, zirconium, cobalt,copper, aluminum, lead, platinum, tin, silver, gold), a conductingmetallic compound material (e.g., tantalum nitride, titanium nitride,tantalum carbide, titanium carbide, titanium aluminum carbide, tungstensilicide, tungsten nitride, ruthenium oxide, cobalt silicide, nickelsilicide), carbon nanotube, conductive carbon, graphene, or dopedpolycrystalline or amorphous silicon, germanium, silicon germanium, orany suitable combination of these materials. The gate dielectric 315 mayinclude an oxide such as silicon oxide, or a high-k dielectric material,or any combination of these materials. Examples of high-k materialsinclude but are not limited to metal oxides such as hafnium oxide,hafnium silicon oxide, hafnium silicon oxynitride, lanthanum oxide,lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide,zirconium silicon oxynitride, tantalum oxide, titanium oxide, bariumstrontium titanium oxide, barium titanium oxide, strontium titaniumoxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, andlead zinc niobate. The high-k may further include dopants such aslanthanum, aluminum. The charge collector dielectric layer 390 mayinclude a dielectric such as silicon oxide, silicon oxynitride, siliconnitride, SiCO, SiOCN, SiCOH, SiBCN, or any suitable combination of thosematerials.

The radiation sensor 300 may also include a first source/drain region330 formed on the substrate 305, the pair of fin structures 310 beingformed on the first source/drain region 330. The radiation sensor 300may also include a second source/drain region 340 formed on an uppersurface of the pair of fin structures 310.

The radiation sensor 300 may also include a bottom spacer 350 formed onthe first source/drain region 330, the gate 320 being formed on thebottom spacer 350, and a top spacer 360 formed on the gate 320, thesecond source/drain region 340 being formed on the top spacer 360.

As illustrated in FIG. 3, when radiation (e.g., electromagneticradiation, such as gamma rays, X-rays and the higher energy range ofultraviolet light) is incident on the charge collector dielectric layer390, radiation charges RC (e.g., radiation particles) may become trappedin a portion of the charge collector dielectric layer 390 adjacent tothe pair of fin structures 310.

The portion of the charge collector dielectric layer 390 containing theradiation charges RC may thus serve as a back gate, modulating thetransistor characteristics (e.g., the threshold voltage (Vt)) ofradiation sensor 300. That is, for example, a threshold voltage Vt ofthe radiation sensor 300 may shift as a function of radiation dose(e.g., the amount of radiation to which the radiation sensor 300 isexposed, or the amount of radiation incident on the charge collectordielectric layer 390), and the gate 320 may be operable to sense theshifting of the threshold voltage (Vt) of the radiation sensor 300.

FIG. 4 provides a graph 400 illustrating a property (e.g.,characteristic) of the radiation sensors 200, 300, according to anexemplary aspect of the present invention.

In the graph 400, the abscissa represents the gate voltage (Vg) of theradiation sensor 200, 300, and the ordinate represents the logarithm ofthe drain current (Id). Further, the line 410 indicates the propertiesof the radiation sensor 200, 300 before the radiation sensor 200, 300 isexposed to radiation, and the line 420 indicates the properties of theradiation sensor 200, 300 after the radiation sensor 200, 300 is exposedto radiation.

As illustrated in FIG. 4, the logarithm of the drain current (Id) isgenerally greater after the radiation sensor 200, 300 is exposed toradiation (e.g., line 420) than before the radiation sensor 200, 300 isexposed to radiation (e.g., line 410).

Another exemplary aspect of the present invention is directed to asemiconductor device including a radiation sensor (e.g., a plurality ofradiation sensors) and a VFET (e.g., a plurality of VFETs) formed on thesame substrate (e.g., the same semiconductor chip).

Referring again to the drawings, FIG. 5 illustrates a semiconductordevice 501, according to an exemplary aspect of the present invention.

As illustrated in FIG. 5, the semiconductor device 501 includes asubstrate 505 including a sensor region SR, and a VFET region VR formedadjacent to the sensor region SR. The sensor region SR of thesemiconductor device 501 includes a radiation sensor 500 (e.g.,plurality of radiation sensors 500) which may be similar in structureand function to the radiation sensor 300, and the VFET region VRincludes a VFET 1500 (e.g., a plurality of VFETs 1500) formed on thesame semiconductor chip (e.g., substrate 505).

The radiation sensor 500 includes a pair of fin structures 510 includingsemiconductor material formed on a substrate 505. The radiation sensor500 also includes a gate 520 formed on an inner side 510 a of the pairof fin structures 510, and a charge collector dielectric layer 590formed on an outer side 510 b of the pair of fin structures 510.

The radiation sensor 500 may also include a gate dielectric 515 formedbetween the gate 520 and the inner side 510 a of the fin structures 510.The gate 520 may include a conductive material such as a metal (e.g.,tungsten, titanium, tantalum, ruthenium, zirconium, cobalt, copper,aluminum, lead, platinum, tin, silver, gold), a conducting metalliccompound material (e.g., tantalum nitride, titanium nitride, tantalumcarbide, titanium carbide, titanium aluminum carbide, tungsten silicide,tungsten nitride, ruthenium oxide, cobalt silicide, nickel silicide),carbon nanotube, conductive carbon, graphene, or doped polycrystallineor amorphous silicon, germanium, silicon germanium, or any suitablecombination of these materials. The gate dielectric 515 may include anoxide such as silicon oxide, or a high-k dielectric material, or anycombination of these materials. Examples of high-k materials include butare not limited to metal oxides such as hafnium oxide, hafnium siliconoxide, hafnium silicon oxynitride, lanthanum oxide, lanthanum aluminumoxide, zirconium oxide, zirconium silicon oxide, zirconium siliconoxynitride, tantalum oxide, titanium oxide, barium strontium titaniumoxide, barium titanium oxide, strontium titanium oxide, yttrium oxide,aluminum oxide, lead scandium tantalum oxide, and lead zinc niobate. Thehigh-k may further include dopants such as lanthanum, aluminum. Thecharge collector dielectric layer 590 may include a dielectric such assilicon oxide, silicon oxynitride, silicon nitride, SiCO, SiOCN, SiCOH,SiBCN, or any suitable combination of those materials.

The radiation sensor 500 may also include a first source/drain region530 formed on the substrate 505, the fin structure 510 being formed onthe first source/drain region 530. The radiation sensor 500 may alsoinclude a second source/drain region 540 formed on an upper surface ofthe fin structure 510.

The radiation sensor 500 may also include a bottom spacer 550 formed onthe first source/drain region 530, the gate 520 being formed on thebottom spacer 550, and a top spacer 560 formed on the gate 520, thesecond source/drain region 540 being formed on the top spacer 560.

The VFET 1500 also includes a pair of fin structures 1510 includingsemiconductor material formed on a substrate 505, and a gate 1520 formedon an inner side 1510 a of the pair of fin structures 1510 and on anouter side 1510 b of the pair of fin structures 1510. The VFET 1500 alsoincludes an interlayer dielectric 1590 formed on the gate 1520 (e.g., onthe substrate 505).

The VFET 1500 may also include a gate dielectric 1515 formed between thegate 1520 and the inner side 1510 a of the fin structures 1510 and onthe outer side 1510 b of the fin structures 1510, a first source/drainregion 1530 formed on the substrate 1505, the fin structures 1510 beingformed on the first source/drain region 1530, a second source/drainregion 1540 formed on an upper surface of the fin structures 1510, abottom spacer 1550 formed on the first source/drain region 1530, thegate 1520 being formed on the bottom spacer 1550, and a top spacer 1560formed on the gate 1520, the second source/drain region 1540 beingformed on the top spacer 1560.

As illustrated in FIG. 5, the semiconductor device 501 may also includean isolation region 509 (e.g., shallow trench oxide (STI)) which isformed in the substrate 505 between the radiation sensor 500 and theVFET 1500. As further illustrated in FIG. 9, the isolation region 509may include, for example, a portion of the charge collector dielectriclayer 590 or the interlayer dielectric 1590.

Another exemplary aspect of the present invention may provide a methodof forming a semiconductor device including both radiation sensors andVFETs, using substantially the same processing steps. In this exemplaryaspect, the radiation sensor may retain the basic vertical transistorstructure, but a gate on one side of fins is replaced with oxide tocollect radiation particles.

As illustrated in FIG. 5, when radiation (e.g., electromagneticradiation, such as gamma rays, X-rays and the higher energy range ofultraviolet light) is incident on the charge collector dielectric layer590, radiation charges RC (e.g., radiation particles) may become trappedin a portion of the charge collector dielectric layer 590 adjacent tothe pair of fin structures 510.

The portion of the charge collector dielectric layer 590 containing theradiation charges RC may thus serve as a back gate, modulating thetransistor characteristics (e.g., the threshold voltage (Vt)) ofradiation sensor 500. That is, for example, a threshold voltage Vt ofthe radiation sensor 500 may shift as a function of radiation dose(e.g., the amount of radiation to which the radiation sensor 500 isexposed, or the amount of radiation incident on the charge collectordielectric layer 590), and the gate 520 may be operable to sense theshifting of the threshold voltage (Vt) of the radiation sensor 500.

FIG. 6 illustrates a method 600 of forming a radiation sensor accordingto an exemplary aspect of the present invention.

As illustrated in FIG. 6, the method 600 includes forming (610) aplurality of vertical field effect transistors (VFETs) on a logic regionand sensor region of a substrate, forming (620) a mask on the logicregion, so as to expose the sensor region, removing (630) a gate from anouter side of a pair of fin structures of a VFET in the sensor region,and forming (640) a charge collector dielectric layer on the outer sideof the pair of fin structures.

It is noted that the term “logic region” as used herein, should beunderstood to mean any region outside of the sensor region and differentfrom the sensor region. The “logic region” includes transistors withdouble-gated VFETs which can be used for a variety of applications suchas logic, memory, anology, input-output, etc.

In an exemplary aspect of the present invention, the method 600 mayinclude modifying the plurality of VFETs in the sensor region to form aplurality of radiation sensors in the sensor region, the modifying ofthe plurality of VFETs including the forming of the mask, the removingof the gate and the forming of the charge collector dielectric layer.

FIGS. 7A-7D illustrate a method 701 of forming a radiation sensor,according to another exemplary aspect of the present invention.

In particular, FIG. 7A illustrates a forming of a plurality of VFETs700, 1700, according to an exemplary aspect of the present invention.

As illustrated in FIG. 7A, the method 701 may include forming aplurality of VFETs 700, 1700 on a substrate 705. For example, theforming of the plurality of VFETs 700, 1700 may include forming a firstsource/drain region 730, 1730 on a substrate 705, forming a pair of finstructures 710, 1710 including semiconductor material on the firstsource/drain region 730, 1730, respectively, forming a gate dielectric715, 1715 on an inner side 710 a, 1710 a of the pair of fin structures710, 1710, and on the outer side 710 b, 1710 b of the pair of finstructures 710, 1710 (e.g., wrapping the gate dielectric 715, 1715around the pair of fin structures 710, 1710), forming a gate 720, 1720on the gate dielectric 715, 1715 on the inner side of the pair of finstructures 710, 1710, and on the outer side of the pair of finstructures 710, 1710, and forming a second source/drain region 740, 1740on an upper surface of the pair of fin structures 710, 1710.

Further, a bottom spacer 750, 1750 may be formed on the firstsource/drain region 730, 1730, the gate 720, 1720 being formed on thebottom spacer 750, 1750, and a top spacer 760, 1760 formed on the gate720, 1720, the second source/drain region 740, 1740 being formed on thetop spacer 760, 1760. An interlayer dielectric 1790 is formed on boththe VFETs 700, 1700 (e.g., covers both the VFETs 700, 1700).

Thus, for example, the plurality of VFETs 700, 1700 (double-gated andinsensitive to radiation) may be formed by a standard VFET formationflow process, so that a structure of the VFET 700 is substantiallysimilar to the structure of the VFET 1700. In particular, each of theVFETs 700, 1700 may include a pair of fin structures 710, 1710 with amerged first source/drain region 730, 1730 beneath the pair of finstructures 710, 1710, and a merged second source/drain region 740, 1740on top of the pair of fin structures 710, 1710.

FIG. 7B illustrates an etching of the VFET 700, according to anexemplary aspect of the present invention. As illustrated in FIG. 7B, amask 702 (e.g., a hardmask such as silicon nitride) is formed on theVFET 1700 (e.g., VFET region of the substrate 705), so that the VFET 700(e.g., sensor region of the substrate 705) is exposed. Then, theinterlayer dielectric 1790 on the VFET 700 is etched by using the mask702 so as to expose the gate 720 on the outer side 710 b of the pair offin structures 710.

FIG. 7C illustrates another etching of the VFET 700, according to anexemplary aspect of the present invention. As illustrated in FIG. 7C,the gate 720 and the gate dielectric 715 on the outer side 710 b of thepair of fin structures 710 are removed by etching, by using the mask702.

FIG. 7D illustrates the forming of a charge collector dielectric layer790 (e.g., oxide layer) formed on the outer side 710 b of the pair offin structures 710 in the VFET 700, according to an exemplary aspect ofthe present invention. The charge collector dielectric layer 790 may beformed over the first source/drain region 730, the second source/drainregion 740, and contacting the surface of the outer side 710 of the pairof fin structures 710. The charge collector dielectric layer 790 maythen be planarized to have an upper surface which is co-planar with anupper surface of the second source/drain region 740.

Thus, the resulting structure of the method 700 may be radiation sensor500 of the semiconductor device 501 which is illustrated in FIG. 5. Thatis, by the method 700, the VFET 700 may be transformed into theradiation sensor 500 (single-gated and sensitive to radiation) which isformed on the sensor region SR of the substrate 505 adjacent to a VFETregion VR.

Thus, the method 700 may include a process flow which includes makingboth sensor VFETs and logic VFETs by the same flow, using a mask tocover the logic region of the substrate and open the sensor region ofthe substrate, removing the gate (and gate dielectric) from the outersides of sensor FET, and filling charge collector dielectric material(e.g., oxide) on the outer side of the sensor FET.

That is, the method 700 may form radiation sensors with verticaltransistors. The radiation sensor retains the basic vertical transistorstructure but the gate on one side of fins is replaced with oxide whichmay be used collect radiation particles. When radiation particles aretrapped in the oxide, the oxide serves as a back gate of the verticaltransistor. The transistor characteristics such as threshold voltage(Vt) shift as a function of radiation dose, and the gate on the otherside of fins may be used to sense the shift in Vt.

With its unique and novel features, the present invention provides aradiation sensor that may be formed by modifying a vertical field effecttransistor (VFET).

While the invention has been described in terms of one or moreembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theappended claims. Specifically, one of ordinary skill in the art willunderstand that the drawings herein are meant to be illustrative, andthe design of the inventive method and system is not limited to thatdisclosed herein but may be modified within the spirit and scope of thepresent invention.

Further, Applicant's intent is to encompass the equivalents of all claimelements, and no amendment to any claim the present application shouldbe construed as a disclaimer of any interest in or right to anequivalent of any element or feature of the amended claim.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor fin structure formed on a substrate; a gate dielectricformed on a first side of the semiconductor fin structure; and adielectric layer formed on a second side of the semiconductor finstructure opposite the first side, and configured to collect charges ofradiation incident on the dielectric layer.
 2. The semiconductor deviceof claim 1, wherein the semiconductor device comprises a radiationsensor, and wherein the semiconductor fin structure comprisessemiconductor material, and the dielectric layer comprises a chargecollector dielectric layer.
 3. The semiconductor device of claim 2,wherein the semiconductor fin structure comprises a pair ofsemiconductor fin structures.
 4. The semiconductor device of claim 2,further comprising: a gate formed on the gate dielectric.
 5. Thesemiconductor device of claim 4, wherein the gate comprises a metal gateand the gate dielectric comprises a high-k dielectric material.
 6. Thesemiconductor device of claim 4, wherein the radiation sensor comprisesa modified vertical field effect transistor (VFET), a threshold voltageof the modified VFET shifting as a function of radiation dose, and thegate being operable to sense the shifting of the threshold voltage. 7.The semiconductor device of claim 4, further comprising: a secondsource/drain region formed on an upper surface of the semiconductor finstructure.
 8. The semiconductor device of claim 7, further comprising: abottom spacer formed on the first source/drain region, the gate beingformed on the bottom spacer; and a top spacer formed on the gate, thesecond source/drain region being formed on the top spacer.
 9. Thesemiconductor device of claim 2, wherein the charge collector dielectriclayer comprises an oxide layer.
 10. The semiconductor device of claim 2,further comprising: a first source/drain region formed on the substrate,the semiconductor fin structure being formed on the first source/drainregion.
 11. The semiconductor device of claim 2, further comprising: avertical field effect transistor (VFET) formed on the substrate adjacentto the radiation sensor.
 12. A method of forming a semiconductor device,the method comprising: forming a semiconductor fin structure on asubstrate; forming a gate dielectric on a first side of thesemiconductor fin structure; and forming a dielectric layer on a secondside of the semiconductor fin structure opposite the first side, thedielectric layer being configured to collect charges of radiationincident on the dielectric layer.
 13. The method of claim 12, furthercomprising: forming a radiation sensor comprising the semiconductorstructure, the gate dielectric and the charge collector layer, thesemiconductor structure including a fin structure comprisingsemiconductor material, and the dielectric layer comprising a chargecollector dielectric layer.
 14. A method of forming a semiconductordevice, the method comprising: forming a first fin structure on a firstregion of a substrate; forming a second fin structure on a second regionof a substrate; forming a first gate on an inner side of the first finstructure which faces the second fin structure, and a second gate on anouter side of the first fin structure which is opposite the inner side;and replacing the second gate with a dielectric layer.
 15. The method ofclaim 14, further comprising: forming a first transistor including thefirst fin structure; and forming a second transistor including thesecond fin structure, wherein the forming of the first transistorcomprises forming a first plurality of vertical field effect transistors(VFETs) on the first region, and the first region comprises a sensorregion of the substrate, wherein the second region comprises a logicregion of the substrate, wherein the replacing of the second gatecomprises: forming a mask on the logic region, so as to expose thesensor region; removing the second gate from the outer side of the firstfin structure; and forming the dielectric layer on the outer side of thefirst fin structure, and wherein the forming of the dielectric layercomprises forming a charge collector dielectric layer on the outer sideof the first fin structure.
 16. The method of claim 15, furthercomprising: before the removing of the gate, etching an interlayerdielectric film of the VFET in the sensor region by using the mask. 17.The method of claim 16, wherein the etching of the interlayer dielectricfilm exposes the second gate on the outer side of the first finstructure.
 18. The method of claim 17, wherein the removing of thesecond gate comprises etching the exposed gate to expose a gatedielectric.
 19. The method of claim 15, wherein the charge collectordielectric layer comprises an oxide layer.
 20. The method of claim 15,wherein the forming of the first transistor comprises forming a pair offirst transistors including a pair of first fin structures,respectively, and wherein the replacing of the second gate comprisesreplacing a pair of second gates on the outer sides of the pair of firstfin structures with a charge collector dielectric layer, respectively.